Machines for boring and finishing cylindrical holes, such as engine cylinder bores, use a tool having abrasive strips mounted on a cylindrical body. As these tools wear, they are generally adjusted radially outward to compensate for the depletion of the abrasive surface. The wear compensating adjustment mechanism forms part of the tool body and comes in many shapes and sizes, for example the tool shown and described in U.S. Pat. No. 4,075,794. These tools consist of a mandrel which connects to the machine spindle at one end and is constructed with an abrasive head at the other. A connecting rod connects to an adjustment mechanism within the abrasive head to bias the abrasive elements radially outward against the work piece. The adjustment can be accomplished automatically as shown in the ""794 patent or manually as shown in the reference Gross, U.S. Pat. No. 2,787,865.
The particular tools, shown in the above referenced patents, are used in honing machines for the construction of precision bores, such as piston cylinders in automotive engines, transmission pinion gears, and similar applications. In the past, such machines have been dedicated to specific tasks in association with particular production runs. With the onset of modern manufacturing concepts such as Just in Time Manufacturing, lean manufacturing, and other inventory reduction methods, there is a need to apply flexible machining systems to the tasks that were previously performed by dedicated machinery. Flexible machine systems generally employ computer numerically controlled (CNC) equipment capable of performing multiple varied operations on multiple workpieces. It is a purpose of this invention to provide a honing tool for use with CNC machinery.
A common feature of CNC machines is the use of through the tool coolant dispersion for lubricating and cooling the abrasives during use. It is another purpose of this invention to utilize the cooling fluid of CNC machines to provide actuation of the abrasive stone adjustment.
One attempt to utilize coolant fluid to actuate the adjustment of abrasive elements is shown in U.S. Pat. No. 5,800,252. In this system a revamped tool is constructed which provides a supply of pressurized liquid down the length of the mandrel to the underside of the abrasive elements. This design requires a specially designed fluid supply and tool. It is a purpose of this invention to provide a honing tool for CNC machines which can be simply retrofitted to provide fluid actuation of the abrasive elements.
A tool is constructed for a CNC machine station to perform a honing operation as part of a flexible machining system. The tool is an assembly of a tool body which holds the abrasive elements, a mandrel which supports the tool body, and a coupling which connects the tool to the CNC machine as is well known. Commonly the abrasive elements are positioned in axially extending slots positioned circumferentially about the periphery of the tool body. The abrasive elements engage a wedge shaped cam that is designed to convert an axial force into a radial force to move the abrasive elements radially. The abrasive elements are spring biased radially inward to provide both extension and retraction of the abrasive elements. The radial force is generally exerted by the motion of a shaft extending axially through the mandrel to engage the cam surfaces.
According to the system of this application, a closed pressure chamber is constructed at the spindle end of the mandrel. A piston is attached to the upper end of the adjustment shaft and mounted for movement within the chamber. The piston and axial shaft comprise the adjustment actuator assembly for the tool. The piston is spring biased towards the spindle end of the chamber. A supply of pressurized fluid or air is supplied to the chamber to force the piston to move along the axis of the mandrel against the force of the spring. The piston and chamber are designed to provide a continuous bias at the tool holders urging the abrasive elements radially outward. The piston chamber is designed to accept the pressure of liquid or gas from a pump or a regulator could be inserted in to the supply channel to control the pressure. The fluid supply is preferably coolant fluid, and will be explained as coolant in this document, is already available at the spindle of the CNC machine.